• Energy Research

This paper proposes a simulation model to calculate short-circuit fault currents in a DC light rail system with a wayside energy storage device. The simulation model was built in MATLAB/Simulink using the electrical information required to define a comprehensive DC traction power rail system. The short-circuit fault current results obtained from the simulation model were compared with hand calculation results obtained using EN 50123-1 guidance. The relative error was 1.02%, which validates the model. A case study was carried out for a 1500 V DC light rail system. In the case study, a method was proposed to assess the DC protection and the withstand and breaking capacity of the DC circuit breakers for maximum current and distant faults. A traction power modeling simulation was conducted for the 1500 V DC light rail system to calculate the maximum load current in the analyzed electrical sections. It is concluded that the proposed simulation model and fault methodology can be used for DC protection settings calculations and DC circuit breaker rating analysis.

This paper presents the concept of using electric vehicles (EVs) as a countermeasure to deal with the negative effects of power rationing when electricity demands become difficult to meet due to unfavorable electrical system operating conditions. At present, an energy storage is widely used to maintain the stability of electricity supply in facilities whose main source of energy is renewable energy sources (RESs). However, we must not forget that electric vehicles are also electricity storage facilities, but they are not always available due to their mobility. With properly developed strategies, they can be used in electricity management processes, for example, by reducing their consumption during charging using smart charging technology, or by providing electricity from their batteries using vehicle-to-building (V2B) technology. Thus, this article presents a research methodology that treats electric vehicles as a remedy for eliminating power constraints. It consists of five main steps, including two algorithms for deciding how to deploy EVs during power rationing periods. An efficiency factor for eliminating these constraints was also introduced. The results showed that the use of smart charging or V2B technology in EVs can reduce the number of potential hours in which certain power levels are exceeded by up to several tens of percent. This means that in the future, with the significant development of electromobility, such a way of dealing with power constraints could be an alternative to conventional solutions like diesel generators.

This paper investigates the benefits of using the on-board energy storage devices (OESD) and wayside energy storage devices (WESD) in light rail transportation (metro and tram) systems. The analysed benefits are the use of OESD and WESD as a source of supply in an emergency metro scenario to safely evacuate the passengers blocked in a metro train between stations; the use of OESD for catenary free sections, the benefits of using the WESD as an energy source for electrical car charging points and tram traction power supply; the benefits of using a central communication system between trams, cars, WESD and electrical car charging points. The authors investigated the use of: OESD with batteries for a catenary free section for different scenarios (full route or a catenary free section between two stations); the charge of OESD between stations (in parallel with tram motoring) to decrease the charging dwell time at stations and to help in achieving the operational timetable; the thermal effect of the additional load on the overhead contact system (OCS) when the tram is charging between stations; the sizing of OESD and WESD for emergency feeding in a metro system. The authors investigated the use of the WESD as a source of energy for the electrical car charging points to reduce the car pollution and carbon emissions. Presented in the paper is the enhanced multi train simulator with WESD prepared for the analyses conducted. The paper describes the DC electrical solver and WESD control method. A validation of the software has been conducted in regard to the substation voltage, WESD energy balance and WESD control.

The energy transition toward low-carbon electricity systems has resulted in a steady increase in RESs. The expansion of RESs has been accompanied by a growing number of energy storage systems (ESSs) that smooth the demand curve or improve power quality. However, in order to investigate ESS benefits, it is necessary to determine their reliability. This article proposes a four-state reliability model of a battery ESS operating with a PV system for low-voltage grid end users: households and offices. The model assumes an integration scenario of an ESS and a PV system to maximize autoconsumption and determine generation reliability related to energy availability. The paper uses a simulation approach and proposes many variants of power source and storage capacity. Formulas to calculate the reliability parameters—the intensity of transition λ, resident time Ti, or stationary probabilities—are provided. The results show that increasing the BESS capacity above 80% of daily energy consumption does not improve the availability probability, but it may lead to an unnecessary cost increase; doubling the PV system capacity results in a decrease in the unavailability probability by almost half. The analysis of the results by season shows that it is impossible to achieve a high level of BESS reliability in winter in temperate climates.

Accurate dynamic models of supercapacitors (SCs) are a basis for the design, control and exploitation of the hybrid energy storage systems for electric vehicles. This paper concerns a fractional model of SC impedance, based on the Cole–Cole equation describing relaxation in electric double layer. This article provides a new method of identifying the parameters of fractional order model of SC impedance, performed without disconnecting the SC module from the energy storage system. The test drive for this purpose needs only the respect a few simple recommendations. The article presents the conditions of the mentioned test drive that will ensure the frequency spectra of the recorded signals lying in the bandwidth necessary for the correct identification of the model parameters. These parameters are determined by means of the Nelder–Mead simplex optimization method. The results of the identification described by the time method coincide with those obtained in the frequency domain. It has been shown in the last part of the article that the real energy losses in these systems significantly exceed the losses determined only on the basis of the nominal capacity and series equivalent resistance (ESR), to which the SC catalogue data are usually limited. This paper also provides an auxiliary frequency criterion for the selection of SCs intended for energy storage systems of electric vehicles.

The functioning of universities during the energy transition can be quite a challenge for them. On one hand, it is necessary to pursue a sensible policy of sustainable development based on the growth of their own renewable energy sources and electricity storage facilities. The aim of such measures is to increase self-consumption and ensure partial energy self-reliance while reducing carbon dioxide emissions into the atmosphere. On the other hand, the current geopolitical situation has indicated significant problems in the energy sectors of European Union countries. From the point of view of decision-makers at universities, the main concern should be ensuring the continuity of the operation of such a facility, including ensuring the energy security of the sites under management. Thus, it is necessary to merge these two areas and consider the development of an energy management strategy on university campuses oriented towards the development of distributed generation resources. For this purpose, one of the methods of multi-criteria decision aiding the ELECTRE I was used. As a result of the analyses, an energy management strategy was established for the main campus of the Warsaw University of Technology, which simultaneously ensures energy security and sustainability efforts.

Abstract This paper proposes a simple and easily optimizable mathematical representation of an energy management strategy (EMS) for the hybrid energy storage system (HESS) in EV. The power of each device in the HESS is provided as a continuous function of load power called γ. Two strategies based on the proposed method, one incorporating fixed coefficients of the γ function (GBS) and one with coefficients optimized by a genetic algorithm (GAS) in real-time using a backward time window, are tested and compared to the rule-based strategy (RBS) and battery storage system. The calculations are made for an electric car with a LiFePO4 battery-supercapacitor HESS. The analyzed parameters are: energy consumption, RMS and maximum current rates of the battery, and the cycle cost of an EV with HESS and a battery-powered EV. The analysis is made in dependence on drive cycle speed and an internal resistance of the battery module. The obtained results show that the GBS and the GAS are able to reduce the RMS current rate by 40% in the NEDC in comparison to battery-powered EV, as well as that maximum current rates do not exceed nominal values. The GAS aims at the minimization of energy consumption. It obtains best results in low speed cycles.

The article discusses the analysis of the possible development of hazards associated with the operation of vehicles equipped with an electric drive using the example of passenger cars. The authors review the problem of the safety of people and property resulting from the occurrence of a fire in an electric passenger car, in the context of fires that have occurred in recent years. Particular attention was paid to the analysis of the state of knowledge concerning the characteristics of the fire progression in an electric car, its heat release rate curve [HRR], total heat release [THR], heat of combustion and factors affecting the fire progression. In this paper, an attempt was made to compare the fire characteristics of an electric car and a passenger car equipped with an internal combustion engine together with an estimation, using CFD simulations, of the impact on the safety of people and property in closed structures such as underground garages or road tunnels. The need for further development of research on electric cars equipped with large lithium-ion batteries in the context of their fire safety is indicated. The authors pay attention to the insufficient amount of data available to understand the fire characteristics of modern electric cars, which would enable the appropriate design of fire safety systems in building structures.